The present invention relates to a polymer composite comprising a polymer and an inorganic additive, more specifically, layers of a swellable material, and to a method for preparing the polymer composite.
Polymer composites comprising a polymer matrix having one or more additives such as a particulate or fiber material dispersed throughout the continuous polymer matrix are well known. The additive is often added to enhance one or more properties of the polymer.
Useful additives include inorganic layered materials such as talc, smectite clays and mica of micron size. These materials can also be referred to as inorganic silicates. Other inorganic layered materials which do not contain silicon may also be used.
A number of techniques have been described for dispersing the inorganic layered material into a polymer matrix. It has been suggested to disperse individual layers, for example, platelets, of the layered inorganic material, throughout the polymer. However, without some additional treatment, the polymer will not infiltrate into the space between the layers of the additive sufficiently and the layers of the layered inorganic material will not be sufficiently uniformly dispersed in the polymer.
To facilitate a more uniform dispersion of the layered inorganic material in the polymer, as described in U.S. Pat. No. 4,889,885, sodium or potassium ions normally present in natural forms of inorganic silicates or mica-type silicates and other multilayered particulate materials are exchanged with onium ions (for example, alkylammonium ions or suitably functionalized organosilanes). This cation exchange process can render the normally hydrophilic mica-type silicates organophilic and expand the interlayer distance of the layered material. An additional process of rendering the mica-type silicates as organophilic is to disperse or synthesize in a glycol or other appropriate solvent. The organophilic mica-type silicates include those materials commonly referred to as organoclays. Other processes may also render the previously hydrophilic mica-type silicate organophilic. Subsequently, the layered material (conventionally referred to as "nanofillers") is mixed with a monomer and/or oligomer of the polymer and the monomer or oligomer polymerized. The nanofiller may also be melt-compounded or melt-blended with polymer. Blending the nanofillers with the monomer, oligomer or polymer results in an increase of the average interlayer distance of the layered material. This increase in the average interlayer distance is referred to as delamination or exfoliation of the layered material.
In WO 93/11190, an alternative method for forming a polymer composite is described in which a layered, particulate material having reactive organosilane compounds is dispersed in a thermoplastic polymer or vulcanizable rubber.
Yet additional polymer composites containing these so-called nanofillers and/or their methods of preparation are described in U.S. Pat. Nos. 4,739,007; 4,618,528; 4,528,235; 4,874,728; 4,889,885; 4,810,734; and 5,385,776; WO 95/14733; WO 93/04117; Chem. Mater. Vol. 6, pages 468-474 and 1719-1725; and Vol. 7, pages 2144-2150; and Chem. Mater., Vol. 8, pages 1584-1587 (1996).
U.S. Pat. No. 5,554,670 describes cross-linked, epoxy-based nanocomposites produced from diglycidyl ether of bisphenol A (DGEBA) and certain specific curing agents. This patent teaches that bifunctional primary or secondary amines do not produce delaminated nanocomposite structures and instead result in opaque composites.
Chem. Mater., Vol. 8, pages 1584-1587 (1996) describes the importance of complete ion-exchange in the formation of organoclays to provide nanocomposites with maximized performance.
However, even with these numerous described composites and methods, it still remains desirable to have an improved method for forming polymer composites derived from a multilayered additive to make composites having improved properties over the polymer alone.